1. Field of the Invention
The present invention relates to a toner for the development of electrostatic images (electrostatic latent images) that are used in image-forming methods such as electrophotography and electrostatic printing.
2. Description of the Related Art
The ubiquity of computers and the growth of multimedia have in recent years created demand for means that can output high-definition full-color images in a wide range of fields from the office to the home.
Use in an office where extensive copying or printing is performed requires a high durability whereby even high count copying or printing does not cause a decline in image quality. Use in the home or a small office, on the other hand, requires the production of high quality images as well as downsizing of the image-forming apparatus in order to economize on space and energy and lower the weight. Additional improvements in toner properties, i.e., environmental stability, member contamination, low-temperature fixability, development durability, and storage stability, have become necessary in order to respond to these requirements.
In the particular case of full-color images, the image is formed by overlaying color toners; however, if the color toners for the individual colors do not undergo similar development, the color reproducibility declines and color unevenness is produced. An influence on the development performance may appear and color unevenness may be produced when the dye or pigment used as the colorant for the toner is precipitated or deposited on the surface of the toner particle.
A fixing performance and color mixability at the time of fixing are crucial for the formation of full-color images. For example, in order to achieve the higher speeds that are in demand, binder resins are selected that are adapted for low-temperature fixability, but these binder resins also exercise a substantial influence on the developing performance and durability of color toners.
Another demand is for means capable of extended use and high-definition full-color image output in a variety of environments that present different temperatures and humidities. Responding to this demand requires a solution for the problem of the changes in the amount of toner charging and changes in the properties of the toner surface that are produced by differences in the temperature and humidity of the use environment. Another problem that must be solved is contamination of such members as the developing roller, charging roller, regulating blade, and photosensitive drum. The development is thus required of a toner that, even during long-term storage in different environments, has a stable charging performance and a stable development durability that is free of the appearance of member contamination.
As one cause of the fluctuations in toner storage stability and amount of charging that are due to temperature and humidity, a phenomenon is produced in which the release agent and/or resin component of the toner migrate out from the interior of the toner particle to its surface (also referred to as “bleed” herebelow), thus causing the properties of the toner surface to change.
Coating the surface of the toner particle with a resin is one means for solving this problem.
A toner having inorganic fine particles firmly fixed to the surface is disclosed in Japanese Patent Application Laid-open No. 2006-146056 as a toner that exhibits an excellent high-temperature storability and an excellent printing durability during image output in a normal-temperature, normal-humidity environment or a high-temperature, high-humidity environment.
However, even though inorganic fine particles are firmly fixed to the toner particles, bleeding by the release agent and/or resin component occurs from gaps between the inorganic fine particles and the inorganic fine particles are liberated due to a deterioration in the durability, and additional improvements with regard to member contamination and the durability in severe environments are thus required.
A method of producing a polymerized toner is disclosed in Japanese Patent Application Laid-open No. H03-089361, this method being characterized by the addition of a silane coupling agent to the reaction system in order to obtain a toner for which the amount of charging has a narrow distribution, the amount of charging exhibits little dependence on the humidity, and colorant and polar substances are not exposed at the toner particle surface.
With this method, however, the amount of deposition of the silane compound at the toner particle surface and/or the hydrolysis and condensation polymerization of the silane compound are inadequate and additional improvements are required with regard to the environmental stability and the development durability.
A method is disclosed in Japanese Patent Application Laid-open No. H09-179341 for controlling the amount of toner charge and forming a high-quality output image independently of the temperature and humidity environment: the disclosed method uses a polymerized toner that contains a silicon compound executed in the form of a continuous thin film at the surface region.
However, the organofunctional groups have a high polarity and the deposition of the silane compound at the toner particle surface and/or the hydrolysis and condensation polymerization of the silane compound are inadequate and the degree of crosslinking is low. Additional improvements are thus required with regard to the image density variations induced by changes in the charging performance at high temperatures and high humidities and by member contamination caused by a deterioration in the durability.
As a toner that improves the flowability, fluidizing agent liberation, low-temperature fixability, and blocking, Japanese Patent Application Laid-open No. 2001-75304 discloses a polymerized toner that has a coat layer formed by attachment among silicon compound-containing particulate masses.
Additional improvements are required, however, with respect to the occurrence of bleeding in which the release agent and/or resin component migrate out from gaps in the silicon compound-containing particulate masses; variations in image density due to changes in the charging performance at high temperatures and high humidities produced by an inadequate amount of deposition of the silane compound at the toner particle surface and inadequate hydrolysis and condensation polymerization of the silane compound; the generation of member contamination due to melt adhesion of the toner; and the storage stability.